This research is aimed at understanding charge transfer across biological interfaces. Biological processes which occur in this interfacial region range from energy transduction to cell-cell interactions. The kinetics of specially designed photo-initiated charge-transfer process are used as probes of the interfacial region. The reactants and conditions are chosen to maximize information about this region and to test our theory of interfacial charge transport. The pigments are oriented porphyrins and the acceptors for electron transfer range from ferricyanide ion to lipid soluble, oriented nitroxides. Proton transfers are studied by having the reduced acceptor find a proton. The proton transfer reactions of bacteriorhodopsin will be studied in suspension and in mono and bilayer systems. The measurements are made by very sensitive, very fast "tunable voltage clamps" and conductance devices of our own design. The light sources are pulsed dye lasers. The analysis uses chemical kinetics and an equivalent electrical circuit containing a novel "chemical capacitance".